have a global variable money and subtract the cost of a house from it when the player buys one..

check if a house is already built in that spot by checking if creation square is overlapping a house, could work..

A lot of it depends on how you are planning to set upyour graphics and your interface, but if you already have trouble answering these relatively simple questions, you might want to start with an easier game first..

I told my dentist I had trouble with my teeth and asked her to fix it without looking in my mouth..